The present invention relates to novel organic molybdenum complexes and their use as multifunctional additives for lubricating compositions. The novel molybdenum compositions of the present invention comprise the reaction products of a long-chain monocarboxylic acid, a mono-alkylated alkylene diamine, glycerides, and a molybdenum source.
Lubricating oils for internal combustion engines of automobiles or trucks are subjected to a demanding environment during use. This environment results in the oil suffering oxidation that is catalyzed by the presence of impurities in the oil such as iron compounds and is also promoted by the elevated temperatures of the oil during use. This oxidation of lubricating oils during use is typically controlled to some extent by the use of antioxidant additives that may extend the useful life of the oil, particularly by reducing or preventing unacceptable viscosity increases.
Further, there have been many attempts to use lubricants to reduce the friction in an internal combustion engine so as to reduce the fuel consumption of the engine. Numerous classes of lubricant additives have been suggested for use as friction modifiers and to increase the energy efficiency provided to an engine by a lubricant.
Molybdenum containing additives are known to deliver a variety of beneficial properties to lubricants. Examples of lubricants that benefit from the addition of molybdenum are passenger car motor oils, natural gas engine oils, heavy-duty diesel oils, and railroad oils. Over the years molybdenum, when used properly, has been shown to deliver improved anti-wear protection, improved oxidation control, improved deposit control, and improved friction modification for fuel economy. There are many examples in the patent literature showing the use of molybdenum additives as antioxidants, deposit control additives, anti-wear additives and friction modifiers. A partial list of molybdenum-containing lubricant patents is provided below:
Numerous oil-soluble molybdenum compounds and their methods of preparation have been described in the art. For example, glycol molybdate complexes are described by Price et al. in U.S. Pat. No. 3,285,942; overbased alkali metal and alkaline earth metal sulfonates, phenates and salicylate compositions containing molybdenum are disclosed and claimed by Hunt et al in U.S. Pat. No. 4,832,857; molybdenum complexes prepared by reacting a fatty oil, a diethanolamine and a molybdenum source are described by Rowan et al in U.S. Pat. No. 4,889,647; a sulfur and phosphorus-free organomolybdenum complex of organic amide, such as molybdenum containing compounds prepared from fatty acids and 2-(2-aminoethyl) aminoethanol are taught by Karol in U.S. Pat. No. 5,137,647; overbased molybdenum complexes prepared from amines, diamines, alkoxylated amines, glycols and polyols are described by Gallo et al in U.S. Pat. No. 5,143,633; and 2,4-heteroatom substituted-molybdena-3,3-dioxacycloalkanes are described by Karol in U.S. Pat. No. 5,412,130.
Existing molybdenum technology, however, suffers from a number of problems that have limited its widespread use in lubricants. These problems include color, oil solubility, cost and corrosion.
Colorxe2x80x94Many molybdenum technologies that appear in the patent literature deliver high levels of color when used even at moderate levels in crankcase oils. A non-discoloring molybdenum source is important because highly colored oils imply to the end consumer that the oil is xe2x80x9cusedxe2x80x9d and therefore not capable of delivering the maximum amount of protection to the engine. When these highly colored molybdenum sources are used at low levels, e.g. 100-150 ppm delivered molybdenum as is typically required for oxidation, deposit and wear control, discoloration is not substantial but may still be visible. However, when these highly colored molybdenum compounds are used at high levels, e.g. 400-1000 ppm delivered molybdenum as is generally required for friction modification, discoloration is often significant. Traditionally, the color of fully formulated crankcase oils has been determined using the ASTM D 1500 color scale. Two types of unacceptable colors are possible. The first type of discoloration results in a dark rating on the D 1500 scale. The amount of acceptable finished lubricant darkening depends on the customer and application. There are no set standards for the amount of discoloration or darkening that is allowed. Generally, D 1500 ratings equal to or greater than 5.0 are considered unacceptable for a finished crankcase oil. Certain customers may find it difficult to market and sell such dark crankcase oils. The second type of discoloration produces xe2x80x9cno matchxe2x80x9d on the D 1500 color scale. These finished lubricants, in addition to showing no match, are also very dark. Again, certain customers may find it difficult to market and sell such dark crankcase oils.
Oil Solubilityxe2x80x94Many commercially available molybdenum additives designed for use in lubricants exhibit limited solubility in the finished lubricant product. For widespread use of a molybdenum product in lubricant applications the product must not only be soluble, at friction modifier treat levels, in the finished lubricant, it must also be soluble in the additive concentrates used to prepare the finished lubricant.
Costxe2x80x94Molybdenum has long been viewed as an expensive additive for crankcase applications. Part of the reason for the high cost stems from the fact that many of the commercial molybdenum products have low levels, e.g. less than 5% by weight, of molybdenum in the additive. In some cases expensive organic ligands or expensive manufacturing processes are used to produce the commercial molybdenum compounds. There is a need for products with higher molybdenum contents that are prepared from lower cost raw materials.
Corrosionxe2x80x94Many molybdenum technologies that appear in the patent literature contain sulfur. The presence of sulfur in various crankcase applications is detrimental because certain types of sulfur are incompatible with elastomer seals and corrosive. Even the less aggressive forms of sulfur can be corrosive in very high temperature crankcase environments where significant amounts of oxygen and water are present. There are also trends to reduce the amount of sulfur present in finished crankcase lubricants. As these trends start to become a reality additives containing sulfur will become less desirable.
It is also well known that certain molybdenum containing friction modifiers function by a decomposition mechanism that results in the formation of a mixed molybdenum sulfide/molybdenum oxide layer on the metal surface of the engine. The molybdenum species that form on the metal surface can vary significantly and their composition is affected by the types of additives in the lubricant and the engine or test design. For example, it is known that molybdenum dithiocarbamates decompose when heated in use to produce products that include free amine and carbon disulfide. Both such products are aggressive towards copper that is present in the engine bearings. Furthermore, free amines are known to be aggressive towards certain types of elastomer seals present in a wide variety of engines. It is therefore desirable from a compatibility standpoint to develop new additives that are low in sulfur and free amines.
All of the above problems suggest a need for a molybdenum additive that has a high molybdenum content, low amine and sulfur content, good oil solubility, and non-discoloring to base oil and finished crankcase oils. It has unexpectedly been found that the molybdenum additives of the present invention provide the above benefits to lubricating compositions without the attendant problems commonly associated with molybdenum additives.
In one aspect, this invention is directed to molybdenum compositions that show excellent oil solubility and a low tendency to color finished crankcase oils. These molybdenum additives comprise the reaction products of a long-chain monocarboxylic acid, a mono-alkylated alkylene diamine, glycerides, and a molybdenum source.
In another embodiment, the present invention is directed to methods for improving the antioxidancy and friction properties of a lubricant by incorporating into the lubricant the novel molybdenum additives of the present invention.
The molybdenum complexes of the present invention comprise the reaction products of a long-chain monocarboxylic acid, a mono-alkylated alkylene diamine, glycerides, and a molybdenum source.
The long-chain monocarboxylic acids suitable for use in the present invention preferably contain at least 8, and more preferably at least 12, carbon atoms. Examples of suitable acids for use in the present invention include fatty acids such as coconut acid, hydrogenated coconut acid, menhaden acid, hydrogenated menhaden acid, tallow acid, hydrogenated tallow acid, and soya acid. Additional long-chain carboxylic acids that may be used include lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachidic acid, behenic acid, erucic acid, oleic acid, linoleic acid, and linolenic acid. Mixtures of acids may also be used and are sometimes preferred. For example, commercial oleic acid is actually a mixture of many fatty acids ranging in carbon chain length from 14 to 20.
The mono-substituted alkylene diamines suitable for use in the present invention are mono-alkylated and contain one secondary amine group and one primary amine group. Examples of some mono-alkylated alkylene diamines that may be used include methylaminopropylamine, methylaminoethylamine, butylaminopropylamine, butylaminoethylamine, octylaminopropylamine, octylaminoethylamine, dodecylaminopropylamine, dodecylaminoethylamine, hexadecylaminopropylamine, hexadecylaminoethylamine, octadecylaminopropylamine, octadecylaminoethylamine, isopropyl-oxo-propyl-1,3-propanediamine, and octyl-oxo-propyl-1,3-propanediamine. Mono-alkylated alkylene diamines derived from fatty acids may also be used. Examples include N-coco alkyl-1,3-propanediamine (Duomeen(trademark) C), N-tall oil alkyl-1,3-propanediamine (Duomeen(trademark) T) and N-oleyl-1,3-propanediamine (Duomeen(trademark) O), all commercially available from Akzo Nobel. Mixtures of mono-alkylated alkylene diamines may also be used.
Glycerides suitable for use in the present invention are of the formula: 
wherein each R is independently selected from the group consisting of H and C(O)Rxe2x80x2 where Rxe2x80x2 may be a saturated or an unsaturated alkyl group having from 3 to 23 carbon atoms. Examples of glycerides that may be used include glycerol monolaurate, glycerol monomyristate, glycerol monopalmitate, glycerol monostearate, and mono-glycerides derived from coconut acid, tallow acid, oleic acid, linoleic acid, and linolenic acids. Typical commercial monoglycerides contain substantial amounts of the corresponding diglycerides and triglycerides. These materials are not detrimental to the production of the molybdenum compounds, and may in fact be more active. Any ratio of mono- to di-glyceride may be used, however, it is preferred that from 30 to 70% of the available sites contain free hydroxyl groups (i.e., 30 to 70% of the total R groups of the glycerides represented by the above formula are hydrogen). A preferred glyceride is glycerol monooleate, which is generally a mixture of mono, di, and tri-glycerides derived from oleic acid, and glycerol. Suitable commercially-available glycerides include HiTEC(copyright) 7133 glycerol monooleate available from Ethyl Corporation which generally contains approximately 50% to 60% free hydroxyl groups.
Molybdenum Incorporationxe2x80x94The source of molybdenum is an oxygen-containing molybdenum compound capable of reacting with the reaction product of the fatty acid, the mono-substituted diamine and the glyceride. The sources of molybdenum include, among others, ammonium molybdate, sodium molybdate, molybdenum oxides and mixtures thereof. A particularly preferred molybdenum source comprises molybdenum trioxide.
The order of reacting the components of the present invention is not critical. The long-chain acid and the diamine may be reacted to form an aminoamide. The aminoamide is then reacted with the glyceride(s) and the molybdenum source. In one embodiment, the long-chain acid and the diamine can be reacted to form an ammonium carboxylate salt. The salt is then reacted with the glyceride(s) and the molybdenum source. In another embodiment, the long-chain acid and the diamine can be reacted to form a mixture of ammonium carboxylate salt and aminoamide. The salt/aminoamide mixture is then reacted with the glyceride(s) and the molybdenum source. In still another embodiment, the long-chain acid, the diamine, the molybdenum source and the glyceride(s) can all be charged to the reactor at one time (i.e., it is not necessary to pre-form the aminoamide or ammonium carboxylate).
The addition of water to these reactions is not required, however, water can facilitate the reaction rate and significantly improve the yields based on molybdenum incorporation. Water should be removed to drive the reaction to completion and maximize the amount of molybdenum incorporated.
The typical molar stoichiometry of the raw materials used to prepared these oil soluble molybdenum compounds is as follows:
An example of a preferred molar stoichiometry is as follows:
The reaction between the long-chain acid and mono-alkylated diamine is typically carried out between 75 and 180xc2x0 C. by combining the two materials and heating with mixing and under a nitrogen atmosphere. The preferred reaction temperature is between 100 and 150xc2x0 C. Reaction times may vary, and typically range from 1 hour to 12 hours. A reaction solvent may be used as long as it does not react with the fatty oil or diamine. The preferred reaction solvents are toluene, xylenes, heptane, and various naphthenic, paraffinic and synthetic diluent oils. The amount of solvent used is not critical but is kept to a minimum for practical purposes. In general, when the reaction times are short and/or when the reaction temperatures are low, the ammonium carboxylate salts are the principal products formed. At higher temperatures and longer reaction times larger quantities of the aminoamide products are formed. Water removal facilitates the formation of the aminoamide products.
An example of a suitable method of molybdenum incorporation is as follows: Molybdenum trioxide, the glyceride(s) and water are added to the aminoamide/ammonium carboxylate reaction mass maintained at approximately 60-80xc2x0 C. The amount of water used is generally equivalent to the amount of molybdenum trioxide used, by weight, but higher levels of water may be used. After addition of the molybdenum trioxide, the glyceride(s) and water, the reaction is slowly heated to reflux temperature with gradual removal of water. Water may be removed by distillation, vacuum distillation, or by azeotropic distillation from a suitable solvent. Suitable solvents include toluene, xylenes, and heptane. The reaction can be monitored by removal of water. The amount of water collected is equal to the amount added plus the amount generated to produce the molybdenum complex. The reaction generally requires 1 to 10 hours. At the end of the reaction period the mixture is cooled, filtered to remove any unreacted molybdenum trioxide and, if used, the solvent is removed by vacuum distillation. In many cases filtration is not required because all of the molybdenum trioxide is reacted. From a practical and cost standpoint, it is desirable to react all of the molybdenum trioxide. The product prepared by this process is a dark amber wax or viscous liquid.
The molybdenum complexes of the present invention are oil-soluble molybdenum compounds substantially free of reactive sulfur. As used herein the term xe2x80x9coil-soluble molybdenum compound substantially free of reactive sulfurxe2x80x9d means any molybdenum compound that is soluble in the lubricant or formulated lubricant package and is substantially free of reactive sulfur. The term reactive sulfur is sometimes referred to as divalent sulfur or oxidizable sulfur. Reactive sulfur also includes free sulfur, labile sulfur or elemental sulfur, all of which are sometimes referred to as xe2x80x9cactivexe2x80x9d sulfur. Active sulfur is sometimes referred to in terms of the detrimental effects it produces. These detrimental effects include corrosion and elastomer seal incompatibility. As a result, xe2x80x9cactivexe2x80x9d sulfur is also referred to as xe2x80x9ccorrosive sulfurxe2x80x9d or xe2x80x9cseal incompatible sulfurxe2x80x9d. The forms of reactive sulfur that contain free, or xe2x80x9cactivexe2x80x9d sulfur, are much more corrosive to engine parts than reactive sulfur that is very low in free or xe2x80x9cactivexe2x80x9d sulfur. At high temperatures and under severe conditions, even the less corrosive forms of reactive sulfur can cause corrosion. It is therefore desirable to have a molybdenum compound that is substantially free of all reactive sulfur, active or less active. By xe2x80x9csolublexe2x80x9d or xe2x80x9coil-solublexe2x80x9d it is meant that the molybdenum compound is oil-soluble or capable of being solubilized under normal blending or use conditions into the lubrication oil or diluent for the concentrate. By xe2x80x9csubstantially freexe2x80x9d it is meant that trace levels of sulfur may be present due to impurities or catalysts left behind from the manufacturing process. This sulfur is not part of the molybdenum compound itself, but is left behind from the preparation of the molybdenum compound. Such impurities can sometimes deliver as much as 0.05 weight percent of sulfur to the final molybdenum product.
As discussed previously, in many cases it is desirable to have an additive low in free amines in order to avoid copper corrosion and potential problems with elastomer seals. In one embodiment of the present invention, the novel molybdenum compounds have a ratio (wt/wt) of nitrogen to molybdenum (N/Mo) of xe2x89xa60.6, preferably xe2x89xa60.4 and more preferably xe2x89xa60.3.
The molybdenum additives of the present invention may be used as antioxidants, deposit control additives, anti-wear additives and/or friction modifiers. The treat rates of the molybdenum additives depend upon the desired finished lubricant properties, however, typically the additives are present in an amount so as to provide at least about 50 ppm, and preferably from about 50 to about 1000 ppm, of molybdenum to the finished lubricant. The concentration of molybdenum in the lubricants according to the invention has no particular upper limit, however, for economic reasons a maximum level of about 1000 ppm is generally preferred although not required.
The molybdenum complexes of the present invention have excellent solubility in a wide variety of basestock types and have a reduced tendency to color finished crankcase oils. Further, the complexes have high molybdenum incorporations, may be prepared from low cost raw materials and have straightforward production processes.
The composition of the lubricant oil can vary significantly based on the customer and specific application. The oil will typically contain, in addition to the molybdenum compounds of the invention, a detergent/inhibitor additive package and a viscosity index improver. In general, the lubricant oil is a formulated oil which is composed of between 65 and 95 weight percent (wt. %) of a base oil of lubricating viscosity, between 0 and 30 wt. % of a polymeric viscosity index improver, between about 5 and 15 wt. % of an additional additive package and typically a sufficient amount of molybdenum complex to provide at least about 50 ppm of molybdenum to the finished lubricant.
The detergent/inhibitor additive package may include dispersants, detergents, zinc dihydrocarbyl dithiophosphates (ZDDP), additional antioxidants, pour point depressants, corrosion inhibitors, rust inhibitors, foam inhibitors and supplemental friction modifiers.
The dispersants are nonmetallic additives containing nitrogen or oxygen polar groups attached to a high molecular weight hydrocarbon chain. The hydrocarbon chain provides solubility in the hydrocarbon base stocks. The dispersant functions to keep oil degradation products suspended in the oil. Examples of commonly used dispersants include hydrocarbyl-substituted succinimides, hydrocarbyl amines, polyhydroxy succinic esters, hydrocarbyl-substituted Mannich bases, and hydrocarbyl-substituted triazoles. Generally, the dispersant is present in the finished oil in an amount between 0 and 10 wt. %.
The detergents are metallic additives containing charged polar groups, such as phenates, sulfonates or carboxylates, with aliphatic, cycloaliphatic, or alkylaromatic chains, and several metal ions. The detergents function by lifting deposits from the various surfaces of the engine. Examples of commonly used detergents include neutral and overbased alkali and alkaline earth metal sulfonates, overbased alkaline earth salicylates, phosphonates, thiopyrophosphonates, and thiophosphonates. Generally, when used, the detergents are present in the finished oil in an amount from about 0.5 to 5.0 wt. %.
The ZDDP""s are the most commonly used antiwear additives in formulated lubricants. These additives function by reacting with the metal surface to form a new surface active compound which itself is deformed and thus protects the original engine surface. Other examples of anti-wear additives include tricresol phosphate, dilauryl phosphate, sulfurized terpenes and sulfurized fats. The ZDDP also functions as an antioxidant. Generally, the ZDDP is present in the finished oil between about 0.25 and 1.5 wt. %. It is desirable from environmental concerns to have lower levels of ZDDP. Phosphorus-free oils contain no ZDDP.
The inclusion of the present molybdenum compounds generally removes the need for supplemental antioxidants. However, a supplementary antioxidant may be included in oils that are less oxidatively stable or in oils that are subjected to unusually severe conditions. The amount of supplemental antioxidant will vary depending on the oxidative stability of the base stock. Typical treat levels in finished oils can vary from 0 to 2.5 wt %. The supplementary antioxidants that are generally used include diarylamines, hindered phenols, hindered bisphenols, sulfurized phenols, sulfurized olefins, alkyl sulfides and polysulfides, dialkyl dithiocarbamates, and phenothiazines.
The base oil according to the present invention may be selected from any of the synthetic or natural oils or mixtures thereof. These oils are typical crankcase lubrication oils for spark-ignited and compression-ignited internal combustion engines, for example natural gas engines, automobile and truck engines, marine, and railroad diesel engines. The synthetic base oils include alkyl esters of dicarboxylic acids, polyglycols and alcohols, poly-alpha-olefins, including polybutenes, alkyl benzenes, organic esters of phosphoric acids, and polysilicone oils. Natural base oils include mineral lubrication oils that may vary widely as to their crude source, e.g., as to whether they are paraffinic, naphthenic, or mixed paraffinic-naphthenic. The base oil typically has a viscosity of about 2 to about 15 cSt and preferably about 2.5 to about 11 cSt at 100xc2x0 C.
The lubricating oil compositions of this invention can be made by adding the molybdenum compound, and any supplemental additives, to an oil of lubricating viscosity. The method or order of component addition is not critical. Alternatively, the molybdenum compounds, along with any additional additives, can be added to the oil as a concentrate.
The lubricating oil concentrate will typically comprise a solvent and from about 2.5 to 90 wt. % and preferably 5 to 75 wt. % of the combination of the molybdenum compound of this invention and the optional supplemental additives. Preferably the concentrate comprises at least 25 wt. % and most preferably at least 50 wt. % of the combination of molybdenum compound and supplemental additives.
In one embodiment, the present invention is directed to a method of improving the oxidation stability of a lubricating oil, wherein said method comprises adding to a lubricating oil an oxidation stability improving amount of the molybdenum complexes of the present invention, wherein said oxidation stability improving amount of said molybdenum complex is effective to improve the oxidative stability of the lubricating oil, as compared to the same lubricating oil except that it is devoid of said molybdenum complex. For improving the oxidation stability of the oil, the molybdenum complex is typically present in the lubricating oil in an amount sufficient to provide at least 50 ppm, preferably at least 100 ppm and more preferably at least 150 ppm, of molybdenum to the finished lubricating oil.
In one embodiment, the present invention is directed to a method of improving the fuel economy of an internal combustion engine, wherein said method comprises using as the crankcase lubricating oil for said internal combustion engine a lubricating oil containing the molybdenum complexes of the present invention, wherein said molybdenum complex is present in an amount sufficient to improve the fuel economy of the internal combustion engine using said crankcase lubricating oil, as compared to said engine operated in the same manner and using the same crankcase lubricating oil except that the oil is devoid of said molybdenum complex. For improving fuel economy, the molybdenum complex is typically present in the lubricating oil in an amount sufficient to provide at least 150 ppm, preferably at least 400 ppm and more preferably at least 800 ppm, of molybdenum to the finished lubricating oil.
In one embodiment, the present invention is directed to a method of reducing deposits in an internal combustion engine, wherein said method comprises using as the crankcase lubricating oil for said internal combustion engine a lubricating oil containing the molybdenum complexes of the present invention, wherein said molybdenum complex is present in an amount sufficient to reduce the weight of deposits in an internal combustion engine operated using said crankcase lubricating oil, as compared to the weight of deposits in said engine operated in the same manner and using the same crankcase lubricating oil except that the oil is devoid of said molybdenum complex. For reducing deposits, the molybdenum complex is typically present in the lubricating oil in an amount sufficient to provide at least 50 ppm, preferably at least 100 ppm and more preferably at least 150 ppm, of molybdenum to the finished lubricating oil. Representative of the deposits that may be reduced using the compositions of the present invention include piston deposits, ring land deposits, crown land deposits and top land deposits.
In one embodiment, the present invention is directed to a method of reducing wear in an internal combustion engine, wherein said method comprises using as the crankcase lubricating oil for said internal combustion engine a lubricating oil containing the molybdenum complexes of the present invention, wherein said molybdenum complex is present in an amount sufficient to reduce the wear in an internal combustion engine operated using said crankcase lubricating oil, as compared to the wear in said engine operated in the same manner and using the same crankcase lubricating oil except that the oil is devoid of said molybdenum complex. For reducing wear, the molybdenum complex is typically present in the lubricating oil in an amount sufficient to provide at least 50 ppm, preferably at least 100 ppm and more preferably at least 150 ppm, of molybdenum to the finished lubricating oil. Representative of the types of wear that may be reduced using the compositions of the present invention include cam wear and lifter wear.